The Greeks had their own script during the Mycenaean era called Linear B even before the first Chinese writing system but that stopped being used after the Bronze Age collapse in Greece and Anatolia.

Afterwards, a new script was created that was based on the Phoenician one but the Greeks modified it by adding vowels which I believe most Afro-Asiatic scripts lacked at the time. Phoenician in turn was based on the Egyptian hieroglyphics.

Wasn't Linear B also based on Hieroglyphics? (sorry if it's a stupid question, I don't know much about the topic). I've read somewhere that Hieroglyphs and/or Sumerian were the first writing systems invented and all the other ones (except of Chinese and Mayan) are somehow derived from it/them.

You might be confusing Cretan hieroglyphics with Egyptian hieroglyphics. Linear B derives from another Greek alphabet system called Linear A, which was developed in the era preceding the Mycenaeans, called the Minoan Civilisation (2700 BCE - 1450 BCE).

all the other ones (except of Chinese and Mayan) are somehow derived from it/them.

Almost all the modern day language scripts are. Latin and Cyrillic scripts derive from the adopted Greek alphabet, which North/South America, maritimes Southeast Asia and Sub-Saharan Africa adopted due to colonialism, Middle East/North Africa/Pakistan uses the Nastaliq alphabet, which derives from Phoenician, Central Asia uses a mix of Nastaliq/Cyrillic alphabets and most of the Indian subcontinent/mainland Southeast Asia uses the Brahmi script, which partially derives from Phoenician alphabet and partly from the native IVC civilisation. Only South Indian (Dravidian) and East Asian alphabets are bereft of any influences of the Phoenician alphabet.

Yeah, Frisian should have been next to Dutch. When answering yes on IJ, there should have been an additional box with â or any of the other circumflex letters that Frisian is fond of but that do not exist in Dutch. Then yes on â should lead to Frisian and no should lead to Dutch.

Oh - to be clear - I have no idea. I’m British, so clearly barely speak any other language. I was just referring to the flowchart. I do speak flowchart exceptionally well, and there are two different versions.

No, because you need to read from left to right. So the "yes" on the left is really coming from the left leading to the ä, it's not an option you would take from the ä, you would never go back that way.

I was curious as well, so as a native Dutch I did some research. Apparently there’re no words in Frisian starting with IJ or these words are names in Dutch. But based on the limited sources I’m not entirely sure

Not accurate regarding Finnish unfortunately, there's no way you'd find 'Å/å' in written Finnish. It's included in our alphabet but only really used in names of people and places. Names of Swedish origin specifically.

Well, you could find Æ and Ø if there are Danish or Norwegian names, Č and Š among others if there are Sami names, bunch more for Turkish, Hungarian etc. But what's the point of the graph if everything's included?